Deep Impact may be more than a movie

Jun 5, 1998

In the
movie Deep Impact astronauts use atomic bombs to try to deflect or destroy a comet on collision with Earth.
Now US scientists have calculated the
effect of such nuclear tipped missiles as part of a research project to study asteroid formation.
They found that the
effects of such an explosion vary depending on the
structure of the
asteroid.
They believe many asteroids that suffer collisions have gravitational fields strong enough to stay together as piles of 'rubble'.
They found that porous asteroids 'damp down' the
effect of the
blast,
and
the
first explosion is vital in defining whether the
rock will disintegrate or not (Nature393 437).

The researchers constructed a mathematical representation of the
irregularly spaced near Earth asteroid Castalia for their calculations.
They assumed it would be made of solid rock,
a pair of solid rocks separated by rubble,
or a 50% porous agglomeration of large boulders.
To simulate a collision they imagined a 8m diameter basalt sphere travelling at 5 kms-1 hitting the
asteroid.
This would impart a explosive force equivalent to a 17 kiloton nuclear device.
They found that in most cases only 10 percent of the
asteroid's mass reached escape velocity,
the
rest of the
material stayed loosely bound in the
area.
A hard rock object on the
otherhand
was more likely to simply split into two.
As well as suggesting that deflecting or destroying asteroids may not be as easy as first thought,
it also suggests that most binary asteroids were formed in collisions this way.